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About UCC25706P

Popescu Bogdan
Prodigy 50 points

Hi guys,

sorry to bother you, I`m trying to build a PWM with this part and I`m experiecing some difficulties, maybe you can help me. I`ve made the layout according to the pin output from the datasheet and with some 10K var potentiometers that I had and with 9 V input there is only a constant 7 V output seen with oscilloscope. 

I haven`t done the soft start part and the tranzistor with the zener that goes to Vdd and FB is that absolutely necessary? or is it optional? The soft start is necessary or otional?

What about the capacitors for Dish and RCl, I`ve put 10 nanof instead of 100 pf is that abosuletely necessary to put 100 picof?

What is the resistance value of ILIM to ground? What are values for the variable resistors if I want to use full 4 mhz and I`m ineterested in very low duty cycle? 

I`m anxiuosly waiting for your reply. 

Thank you very much!

  • 0
    TI__Intellectual 1615 points
    I assume you supply VDD with a 9V with 10k var. because your large series resistor value, you have voltage drop on the resistor you only see 7V on VDD and you see about 7V on gate output
    you don't need zener on VDD if you supply VDD using a well regulated.
    the resistor to FB is required if you use opto coupler feedback. you don't need it if you can feed voltage into FB pin
    you can put what ever the capacitor you want, but you need to follow the equation on page 6
    you need to design the current limit based on your power stage requirements